  echo -e "How old are you? \c"
    read age
    if [ "$age" -lt 0 -o "$age" -gt 120 ]                #等同于 (( age < 0 || age > 120 ))
    then
        echo "You are so old."
    elif [ "$age" -ge 0 -a "$age" -le 12 ]               #等同于 (( age >= 0 && age <= 12 ))
    then
        echo "You are child."
    elif [ "$age" -ge 13 -a "$age" -le 19 ]             #等同于 (( age >= 13 && age <= 19 ))
    then
        echo "You are 13--19 years old."
    elif [ "$age" -ge 20 -a "$age" -le 29 ]             #等同于 (( age >= 20 && age <= 29 ))
    then
        echo "You are 20--29 years old."
    elif [ "$age" -ge 30 -a "$age" -le 39 ]             #等同于 (( age >= 30 && age <= 39 ))
    then
        echo "You are 30--39 years old."
    else
        echo "You are above 40."
    fi
